This invention relates to a method for determining rates of transpiration of certain perfluorocarbons from the body of animals based on a particular physical property of said perfluorocarbons. More particularly, this invention relates to a process for selecting a perfluorocarbon useful as a synthetic blood component which comprises determining the critical solution temperature of said perfluorocarbon and selecting those perfluorocarbons having about 9 to 12 carbon atoms which have critical solution temperatures generally less than 20.degree.-45.degree. C. as further defined below.
The use of perfluorocarbons as synthetic blood components is known, for example, from U.S. Pat. No. 3,911,138 and U.S. Pat. No. 4,105,798. In these and other teachings, it is shown that certain classes of perfluorocarbons, in water emulsion forms, can be administered to animals as a synthetic blood because of the ability of the composition to carry oxygen and CO.sub.2 through the body.
Examples of typical perfluorocarbons which have been tested for their ability to serve as synthetic blood components include perfluoro(1-methyldecalin); perfluoromethylcyclohexane; perfluoro(1,3-dimethylcyclohexane); perfluorodecalin; perfluorodimethyldecalin; perfluoroadamantane; perfluoromethyladamantane; perfluorodimethyladamantane; perfluoro-n-pentane; perfluorohexane; perfluoroheptane; perfluorobicyclo[4.3.0]nonane; perfluorotetrahydrodicyclopentadiene; perfluoro-7-methylbicyclo[4.3.0]nonane; perfluorobicyclo[5.3.0]decane; perfluoro-p-menthane; perfluorotetramethylcyclohexane; perfluoro-n-butylcyclohexane; perfluorotrimethylbicyclo[3.3.1]nonane; and the like. Of these, the cyclic perfluorocarbons are preferred.
Other perfluorocarbons useful as synthetic blood components include, in addition to the above, substituted perfluorocarbons such as other halogen substituted derivatives including mono- or di-bromo, iodo, etc., perfluorocarbons, specifically perfluorooctyl bromide. The presence of a bromine atom in place of a carbon atom is equivalent to the effect of two carbon atoms in vapor pressure. Other hetero perfluorocarbons include perfluoro cyclic amines, and perfluoro cyclic ethers, as well as mixtures of the same with the aforesaid perfluoro paraffinic or cyclic hydrocarbons. Therefore, the term "perfluorocarbon" as used herein is intended to include such diverse compounds and mixtures which may be selected according to the method of this invention.
These compounds and other like candidates, are tested for various properties to determine their suitability as synthetic blood components, including the ability of the body to excrete the perfluorocarbon within a suitable period of time (i.e., the transpiration rate), as shown in the abovementioned patents. These tests are normally determined by either injecting the pure perfluorocarbon into the abdominal cavity and measuring said rate, or by administering the perfluorocarbon in the form of an emulsion into the blood stream and then taking measurements.
As a result of these and other tests, it has been determined over a period of time that the most preferred perfluorocarbons are those having from 9 to 12 carbon atoms. Those compounds with less carbon atoms have too high a vapor pressure for the body to tolerate in that the material comes out of the body too fast and causes gas embolism, while those having too many carbon atoms tend not to have desirable oxygen solubilities, as well as having, in general, too long a residence time in body tissues. Generally speaking, however, each of these determinations has been arrived at empirically, with no known correlation between the physical structure and properties of the perfluorocarbon and its effectiveness as a synthetic blood component.
Although the most preferred perfluorocarbons are those having from 9 to 12 carbon atoms, the process of the invention can be used to screen candidates which have about 9 to 12 carbon atoms, including numbers of carbon atoms less than 8 or greater than 12. A compound having 8 carbon atoms for example might be useful as a component of a synthetic blood composition, in admixture with a compound having 9 to 12 carbon atoms. A person skilled in the art, in the light of the present specification, can with routine experimentation apply the process of the invention to perfluorocarbons generally as disclosed herein.